Bit out of my comfort zone answering these type of questions but will give it a go.
1, Do i take the extended warranty and if so what are the advantages/disadvatages? - No idea, never had a subaru that had a warranty before.
2, Do i have to continue with the metasat tracker ( i want to keep it tracked) or can i switch companies, any ideas? - As above, if they have a lifetime option and you're plan on keeping the car a while go for that. If not switch to a tracker that does give the option.
3. Subaru assist, do i continue or do i just cover it with the likes of the AA/RAC? - RAC for me. You can use about £26 worth of tesco points and get a years get you home cover. Bargain.
The warranty would be a nice to have but if you put the cash to any repairs you know where you are. I'd hate to spend all that money, go to make a claim and they fight you over it.